Method and a dual-array transducer probe for real time mechanical imaging of prostate

ABSTRACT

The present invention relates to a transrectal probe and method for real time mechanical imaging of a prostate. The probe is equipped with dual-array pressure sensors—one on the probe head and another on the shaft of the probe spaced away from the head with an angular and linear offset forming an S-shaped transition between the shaft and the head of the probe. The addition of the shaft pressure sensor array together with orientation tracking sensors allows precise calculation of the current head position throughout the examination of the prostate. Display means are used to guide the user in the proper manipulation of the probe in order to reduce the forces on surrounding tissues and organs and to minimize patient&#39;s discomfort.

CROSS-REFERENCE DATA

This application is a continuing application of a co-pending U.S. patentapplication Ser. No. 11/146,367 filed on Jun. 6, 2005 with the sametitle, which in turn is a continuation-in-part of a co-pending U.S.patent application Ser. No. 11/123,999 filed on May 6, 2005 and entitled“Method and device for real time mechanical imaging of prostate”.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under SBIR Grant 2 R44CA82620-02A1 awarded by the National Institutes of Health, NationalCancer Institute. The government has certain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical devices. Morespecifically, it relates to a mechanical imaging system and process forexamining, mapping, and diagnosing diseases of a palpable organ such asa prostate gland in a male patient, especially the prostate cancer. Itis also applicable more generally to mechanical imaging of palpabletissues, including but not limited to, through natural body openings ina human being, i.e. mouth, ear(s), rectum, and other body cavities. Itis also applicable to determination of a relative stiffness orelasticity of tissues. The term “patient” includes human beings andanimals, both alive and dead that can be subject to mechanical imaging.

The high incidence of prostate cancer, as well as benign prostatichyperplasia (BPH), especially among the older male population, dictatesthe need for effective means of early detection. Prostate cancer is thecause of death in about 30,000 men each year, making it the number twocancer killer of men in the United States, second only to lung cancer.However, if prostate cancer is detected early and treated effectively,the chance of survival of one afflicted with this disease improvessignificantly. Current methods of early diagnosis of prostate cancerinclude digital rectal examination (DRE), measurement of serum levels ofprostate specific antigen (PSA), and transrectal ultrasound (TRUS)examination.

The following discussion provides useful overview of various methodsdescribed in the prior art and applicable to prostate examination andimaging. Substantial prior art is accumulated describing various devicesand techniques using ultrasound for the imaging of the prostate. U.S.Pat. No. 6,561,980 by Gheng describes the methods of processingultrasound images to cause automatic segmentation of prostate, rectum,and urethra once the transverse cross-sectional image of prostate isacquired by ultrasound means. U.S. Pat. No. 6,824,516 by Battendescribes a sophisticated system for examining, mapping, diagnosing, andtreating prostate diseases based on ultrasonic imaging, this patent isincorporated herein in its entirety by reference. U.S. Pat. No.6,778,690 by Ladak describes a method of processing 2D and 3D ultrasoundimages to determine the prostate boundaries and is also incorporatedherein by reference in its entirety as it provides useful imageprocessing methodology.

Unfortunately, to date the experience with TRUS as a means of prostatecancer screening and staging has been disappointing. It adds little toscreening by DRE and PSA, and the small improvement in prostate cancerdetection does not justify its cost. As a screening test, TRUS has a lowspecificity and a high false positive rate. Evaluation of pathologicspecimens shows that a significant fraction of tumors are isoechoic andthus indistinguishable from surrounding tissue, while many palpabletumors could not be visualized by TRUS.

The most sensitive single test for prostate cancer is measurement ofserum PSA levels. However, its positive predictive value is limited. TheDRE alone is even less useful. However, combining the two modalitiesnearly doubles the cancer detection rate. Large-scale studies ofsystematic screening for prostate cancer using PSA, DRE and TRUSconcluded that combining PSA and DRE provided the highest sensitivityand specificity for prostate cancer diagnosis. Therefore, thecombination of the two methods for prostate cancer screening iscurrently recommended by the AUA and American Cancer Society, and hasbeen approved by FDA for patients between the ages of 50 and 75 years.

At the present time, digital rectal examination is the most widely usedmethod of prostate cancer screening. Approximately 30-50% of palpableprostate nodules prove to be malignant upon pathologic evaluation.Screening trials have demonstrated that 70% of men with abnormal DREundergoing radical prostatectomy have organ-confined cancer. A strongassociation between abnormal DRE and prostate cancer mortality has beendemonstrated and it was suggested that screening DRE could prevent asmany as 50-70% of deaths due to prostate cancer. DRE also has been shownto be the most cost efficient prostate screening method, especially whencombined with PSA.

The main disadvantage of DRE is its high degree of subjectivity. Theuser has to instinctively relate what he or she senses by the finger toprevious DRE experience. There may not be a sufficient number of skilledusers available for large-scale mass prostate screenings. Anotherlimitation of DRE is that a physician performing the examination cannotobjectively record the state of the examined prostate. Therefore, it isdifficult to objectively compare the results of consecutive examinationsof the same prostate. The need therefore exists for a device allowingconducting the prostate examination objectively and obtaining resultsconsistently that are independent of the skills of individual operators.

A new method of prostate imaging based on principles similar to those ofmanual palpation has been developed by Sarvazyan et al. and described inthe U.S. Pat. Nos. 6,569,108; 6,142,959; 5,922,018; 5,836,894;5,785,663; and 5,524,636, as well as in a co-pending U.S. applicationSer. No. 11/123,999 all incorporated herein in their entirety byreference. This method, termed Mechanical Imaging, provides the abilityto “capture the sense of touch” and store it permanently for latertemporal correlation and trending. The essence of mechanical imaging ismeasurement of the stress pattern on the surface of the compressedtissue and analyzing the changes of that pattern while moving the sensorarray over the examined tissue. Temporal and spatial changes in thestress pattern provide information on the mechanical structure of theexamined tissue and enable 3D reconstruction of internal structures andmechanical heterogeneities in the tissue. Mechanical imaging is free ofmany of the disadvantages of DRE. Mechanical imaging has been shown toexceed substantially the limits of lesion size and depth detectable byconventional manual palpation techniques [Weiss R., Hartanto V, PerrottiM, Cummings K, Bykanov A, Egorov V, Sobolevsky S. “In vitro trial of thepilot prototype of the prostate mechanical imaging system”, Urology,V.58, No. 6, 2001, p. 1059-1063].

Recently, the American Urological Association issued recommendations tohelp physicians confirm the diagnosis of prostate cancer. According tothese recommendations, a biopsy should be considered for any patientwith an abnormal DRE and elevated PSA. The effectiveness and reliabilityof DRE are highly dependent on the skill of the user, since the fingerdoes not provide a quantitative or objectively verifiable assessment.Thus, there is a great need for a new technology and a device to enablegeneral practitioners and urologists alike to perform a reliable,accurate, sensitive, and quantitative assessment of the prostate using acomputerized palpation-imaging device. Moreover, such accurateassessment of prostate size, shape, and elasticity is also important fordiagnosing and monitoring of prostate cancer and BPH. Mechanical imagingtechnology and the low cost, prostate imaging device should improvesignificantly the ability of minimally trained individuals in primarycare settings to assess, screen, and monitor prostate pathology in areliable and valid manner in a male human, with a minimum of physicaland mental discomfort.

While prior art mechanical imaging devices provided for data collection,the ability to recreate the 2D and 3D images of the prostate werelimited by the insufficiently accurate information obtained from thetransrectal probe with regard to the examined prostate in the course ofexamination. One reason for this is the sub-optimal shape of the probedevice itself. Prior art probes are predominantly round and cylindricalin shape to repeat that of the rectum. Upon compressing the area aboutthe prostate, it is difficult to obtain uniform compression of that areaalone and not load surrounding tissues and organs, especially thesphincter.

The need exists for a novel method and probe adapted for uniformcompression of the desired area in the vicinity of the prostate glandwithout compressing surrounding tissues such as a sphincter. Suchcompression of surrounding tissues and organs would distort datacollection away from the desired area and introduce errors associatedwith tilting the probe and stretching the sphincter or other tissues ofthe rectum.

Another reason for reduced sensitivity is because the prostate can behard to find initially and it can also shift from its original placeduring the examination procedure. Therefore, the prior art methods havea fundamental disadvantage in that as the examination progresses, nomeans are available to properly locate the prostate and then compensatefor the probe position and orientation shift relative for the movingprostate.

The need exists therefore for a prostate examination means and method ofuse designed to eliminate the distortion in the position data of theprostate probe and make it independent of the internal movements of theprostate organ.

Finally, the need exists for devices and methods allowing training ofmedical personnel conducting prostate mechanical imaging.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome theseand other drawbacks of the prior art by providing a novel method anddevice for objective and consistent mechanical imaging of a palpableorgan eliminating the influence of operator's skills on the results ofsuch examination.

It is another object of the present invention to provide a mechanicalimaging device for examination of prostate shaped in such a way as toallow proper compression of the prostate organ only and minimizingdistortions caused by pressing the device against other surroundingtissues and organs.

It is another object of the present invention to provide a mechanicalimaging device for examination of prostate having dual-array pressuretransducer probe, one array on the head of the probe and another on theshaft of the probe.

It is another object of the present invention to provide a probe and amethod of its use allowing teaching the medical personnel the propertechnique of prostate examination.

The method of the invention is based on a method of real time mechanicalimaging of the prostate organ with a probe inserted through a rectum.According to one aspect of the method of the invention, generating atwo- or three-dimensional prostate mechanical image from a plurality ofpressure response data and probe orientation data comprises the generalsteps of:

-   -   locating the prostate under the transrectal probe head pressure        sensor array by first identifying the sphincter with a secondary        pressure sensor array located on a probe shaft, then advancing        the probe until the bladder is reached and then retracting it        somewhat to identify the area of probable location of the        prostate,    -   scanning the prostate by the probe head sensor array by pressing        it repeatedly against the prostate,    -   incorporating newly acquired mechanical prostate information        into a two-dimensional normalized mechanical image of the        prostate, including using of the sphincter as a secondary        reference object,    -   visualizing that two-dimensional normalized mechanical image of        the prostate in real time to reveal possible areas of interest        inside the prostate, and    -   calculating prostate features and constructing of composite        two-dimensional and three-dimensional mechanical prostate        images, using an image recognition technique.

Importantly, the processing of data is preferably conducted by usingdata from both the probe head pressure sensor array (used as a primaryor first source of pressure data) and from shaft pressure sensor array(used as a secondary source of pressure data). This allows moving of theprobe relative to the prostate while maintaining the common identifiedfeatures of each obtained mechanical image. In other words, every timethe probe is moved from one position to the next, the processing meansof the device are adapted to follow certain identifiable features andthe distance from the sphincter from the previous mechanical image tothe next one such that a complete 2D or 3D image may be constructed.That way, there is less need for knowing the absolute position in spaceof both the prostate and the probe in order to accurately relate eachsuccessive pressure pattern to a certain part of the prostate.

In the preferred embodiment, the dual-array probe and the system of theinvention include: an S-shaped probe shaft with pressure sensor arrayfor collecting pressure response data in the vicinity of the sphincter;a probe head pressure sensor array for collecting data in the vicinityof the prostate volume; a probe orientation tracking sensors forcollecting a probe orientation data; a processing apparatus forprocessing the pressure response and orientation data to generatemechanical image data and calculate prostate features; and a displaydevice for representation of at least a two-dimensional image of theprostate.

Importantly, the shape and size of the head pressure sensor array isselected such that it provides for uniform compression of the area ofinterest about the prostate gland and not other areas of the rectum.Further facilitating this aspect of the invention is the S-shaped designand an angular offset between the head of the probe and the shaft of theprobe. Such advantageous shape increases the accuracy of obtainedpressure data and reduces the artifacts caused by inadvertent tilting ofthe probe to avoid sphincter trauma.

Preferably, in order to further increase the accuracy of the results,the probe head orientation and its position relative to examinedprostate is calculated from orientation data recorded from 3D magneticsensors and a 2D accelerometer sensor, and combined with the pressureresponse data recorded from the head pressure sensor array and the shaftpressure sensor array.

As opposed to the devices of the prior art, the present invention takesadvantage combining three independent sources of positioninginformation:

-   -   using the prostate itself as a reference object by providing        real time calculation and visualization of the probe head        positioning relative to the examined prostate    -   having more than one pressure sensor arrays working together in        an integrated manner to take advantage of locating the prostate        in its relationship to a nearby organ, which is more stable in        its position such as sphincter, and finally    -   calculating of probe head position from probe orientation data.

Combining all these sources of information, the device of the inventionprovides calculations including both the orientation and pressureresponse data. The device and method of the present invention arecreated with a design philosophy to create a patient-friendly system,which is easy and intuitive to use by the examining physician. As aresult, the present invention advantageously provides for:

-   -   early prostate cancer detection;    -   quantitative classification of prostate geometrical and        mechanical features;    -   automatic identification of what has changed between successive        examinations;    -   tracking and trending treatment impact for certain treatment        modalities;    -   matching the system output with pathology findings as proof of        system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the subject matter of the presentinvention and the various advantages thereof can be realized byreference to the following detailed description in which reference ismade to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating the functional structure ofthe system in accordance with the present invention,

FIG. 2 is a side view of the probe with a head pressure sensor array, ashaft pressure sensor array, and orientation sensors,

FIGS. 3A and 3B are cross-sectional views of the probe head and theprobe shaft respectively in accordance with the present invention,

FIG. 4 is a diagram of an orientation tracking system used in thepreferred embodiment of the present invention,

FIG. 5 represents an electronic unit schematic diagram of the device,

FIG. 6 is a flow chart describing steps for obtaining diagnosticinformation,

FIG. 7 is a perspective view of the transrectal probe relative to anexamined prostate, illustrating a reference coordinate system havingthree orthogonal axes and probe orientation angles,

FIG. 8 is a flow chart describing steps for composition oftwo-dimensional and three-dimensional prostate mechanical images andcalculating prostate features,

FIG. 9 is an illustration of real time two-dimensional prostate imageand sphincter area mechanical image with relative probe positioning toguide the use of the probe during prostate examination, and

FIG. 10 is an illustration of a three-dimensional prostate mechanicalimage composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A detailed description of the present invention follows with referenceto accompanying drawings in which like elements are indicated by likereference letters and numerals.

Referring now to the drawings, FIG. 1 is a schematic view of a preferredembodiment of a device for generating a mechanical image of athree-dimensional prostate volume from a plurality of data framescorresponding to a scan of the prostate. The device comprises thefollowing major elements:

-   -   a dual-array transrectal probe 3 with incorporated head pressure        sensor array 1 for receiving pressure response data for the        prostate 4 and shaft pressure sensor array 2 for receiving        supplemental pressure response data for a sphincter area 5,    -   electronic unit 6, and    -   a processing and displaying means 7, which may be for example        incorporated into a compact personal computer.

The prostate examination is performed using the following general steps.The patient is instructed to take off all clothes below the waist. Theexamination is preferably performed in the standing position by bendinga patient over the examination table to form a 90-degree angle at thewaist. This novel position allows the muscles in the vicinity of theexamination probe to relax and has yielded better results than otherexamination position. In this position, patient' chest is lying on thetable or another horizontal surface and patient's weight is applied tothe table surface so that leg muscles are free from any tension.Optionally, the patient can also be examined while lying on his side,with his knees bent toward his chest. The probe is preferably enclosedwithin a disposable lubricated cover. During the insertion into therectum, pressure applied to the anal sphincter should be monitored inorder to minimize the level of patient' discomfort. Gentle posteriorpressure is applied as the probe is slowly inserted with the sensorsurface down. Allowing a few seconds for the external and internalsphincter to relax will avoid patient discomfort. Scanning begins in thesagitall plane by first optionally imaging the sphincter used as asupplemental reference organ. Then, the probe is inserted deeper untilthe bladder is visualized. Next, by sliding the probe backwards, theprostate is detected and the probe is positioned in a way that enablesthe device to display the prostate gland surface in the center of thescreen. Once the probe is properly positioned, evaluation of prostate isperformed through a set of multiple pressings on the median sulcus andlateral lobes of the prostate. In certain cases, change in an elevationangle of the probe is required to visualize the prostate.

FIG. 2 is a side view of the preferred embodiment of the transrectalprobe 3 with the head pressure sensor array 1 installed on a probe head21, and with the shaft pressure sensor array 2 installed on a probeshaft 22 attached to the probe handle 24. The most distal probe headsection of the probe has a straight segment containing the head pressuresensor array. The length of this straight segment is preferably chosento be about 25 mm (1 inch) to about 50 mm (2 inches) long. This lengthallows proper coverage of the prostate area without interfering with thebladder or other surrounding tissues.

The shaft 22 of the probe has an S-shaped distal end 22 a designed toprovide a linear offset between the head of the probe and the shaft ofthe probe. When the probe head is compressed against the prostate, theentire probe is moved somewhat down in the direction of the prostate.The presence of this S-shaped section of the probe shaft allows not tocompress tissues and organs surrounding the shaft and only to compressthe prostate by pressing the probe head against thereof. Dimensions ofthe S-shaped distal end of the probe shaft are chosen preferably toensure that the linear offset between the shaft and the head is rangingbetween about 4 mm ( 5/32 of an inch) and 15 mm ( 19/32 of an inch). Inthe most preferred embodiment of the invention this distance is about 10mm.

Additional improvement in the design of the probe is in the angularoffset between the longitudinal axis of the probe head and thelongitudinal axis of the probe shaft. Tilting the shaft axis at about 4to 12 degrees about the head axis further reduces the distortion of thesurrounding tissues and organs when the probe head is pressed againstthe prostate.

Spacing apart the head pressure sensor array and the shaft pressuresensor array at a proper distance allows the probe to be used to findthe estimated position of the prostate using the position of the analsphincter. In the preferred configuration of the dual-array transrectalprobe of the invention, the distance between the head pressure array andthe shaft pressure array is selected to be about 40 mm (1 9/16 inches)to about 80 mm (3⅛ inches) as measured between the centers of therespective pressure sensor arrays. The most preferred distance is about60 mm as this is the average distance between the sphincter and thecenter of a prostate.

Optional elastic disposable cover (not shown) may be used to envelop theentire surface of the probe head 21, probe shaft 22, and partly theprobe handle 24. The probe handle 24 further comprises supplementalpositioning means consisting of a three-axis magnetic sensor 25 and atwo-axis accelerometer sensor 26. The probe also includes an examination“start-stop” button 23. Of note here is the offset of the probe head 21relative to the probe shaft 22. It is designed such that the probebetter fits with the anatomy of a human patient—only the head ispressing against the prostate and the shaft is not loading the sphincterwith a down aimed force. Both the shaft and the head pressure sensorarrays are therefore better adapted to visualize the prostate and thesphincter respectively.

FIG. 3A is a preferred cross-sectional view of the preferably oblongprobe head 21 with surface installed pressure sensors 31 in accordancewith the present invention. As opposed to previously known devices ofthis type having linear pressure sensing arrays, the probe of theinvention is equipped with a two-dimensional pressure sensor array. Aplurality of pressure sensors 32 constitutes the pressure sensing matrixof the head pressure sensor array 1 as shown in FIG. 2. Thetwo-dimensional pressure sensor array 1 serves the following three mainpurposes:

-   -   providing pressure response data in the course of examination of        the prostate,    -   providing information on changes in the probe head position        relative to the prostate deploying a mechanical image        recognition technique, and    -   guiding the user during prostate examination by displaying a        real time complete two-dimensional pressure pattern of the head        pressure sensor array.

Size, grid, and sensor quantity in the head pressure sensor array mayvery. Preferably, the head pressure sensor array has a pressuresensitive area of about 12 to 20 mm wide by 30 to 50 mm long, andincludes over 100 individual pressure sensors. The curvature radius ofthe probe head may vary too, but preferably the curvature radius shouldbe about 10 to 20 mm to provide a uniform stress pattern while pressingagainst the prostate. Individual pressure sensors may be designed to bea piezoelectric, resistive, or quantum tunneling composite pressuretransducer, possibly using micro-machined parts or nano-technologies.Preferably, each pressure sensor includes a capacitive pressuretransducer covered by an elastic compound.

FIG. 3B is a preferred cross-sectional view of the probe shaft 22 withsurface installed supplemental pressure sensors 32 in accordance withthe present invention. A plurality of supplemental pressure sensors 32constitutes the shaft pressure sensor array 2 as shown in FIG. 2. Thisshaft pressure sensor array serves two main purposes:

-   -   receiving supplemental pressure data from the sphincter area        needed to guide the user during prostate examination by        displaying a real time complete two-dimensional pressure pattern        of the shaft pressure sensor array, and    -   calculating a longitudinal position of the probe head relative        to the sphincter allowing an additional correction of the probe        head transversal position relative to the prostate, taking into        account real time changes in probe orientation angles.

As with the head pressure sensor, the size, grid, design, and sensorquantity in the supplemental shaft pressure sensor array may very. Inthe most basic configuration, the shaft pressure sensor array comprisesa single linear pressure array. Better functionality can be achieved byusing two or preferably three linear pressure sensor arrays, especiallywhen they are equally spaced about the outside of the shaft of theprobe. In the most preferred configuration, the shaft pressure sensorarray has a pressure sensitive area all the way around the probe shaftsized to be about 40 mm long and include over 100 individual pressuresensors. A shaft diameter may vary too, but preferably the shaftdiameter is about 12.5 mm. Each individual pressure sensor may be apiezoelectric, resistive, or quantum tunneling composite pressuretransducer, but in the preferred embodiment it is a capacitivetransducer.

FIG. 4 is a diagram of an orientation tracking sensor means used in thepreferred embodiment of the present invention. The orientation trackingmeans includes a three-axis magnetic sensor 25 with orthogonalsensitivity axes M_(x), M_(y), M_(z), and a two-axis acceleration sensor26 having sensitivity axes A_(x), A_(y) accordingly. Importantly,A_(x)-axis is parallel to the M_(x)-axis and A_(y)-axis is parallel tothe M_(y)-axis. Both the magnetic sensor 25 and the acceleration sensor26 are mounted on a platform 41 so that X and Y axes are parallelthereto, which in turn is parallel to the probe head pressure sensingsurface. Preferably, platform 41 is incorporated inside the probe handleto be in the vicinity of the sphincter during prostate examination.Magnetic sensor readings give sensor orientation relative to Earth'smagnetic field. To compensate the magnetic sensor reading for a platformtilt relative to a horizontal plane, which is perpendicular to Earth'sgravity vector, it is necessary to know the platform tilt angles. Thetwo-dimensional accelerometer sensor is used here as a tilt sensor toprovide elevation (φ) and rotation (φ) readings. The X, Y, Z magneticreadings can be traced back to the horizontal plane by applying therotational equations shown below:

Xh=X*cos(φ)+Y*sin(θ)*sin(φ)−Z*cos(θ)*sin(φ)  (1)

Yh=Y*cos(θ)+Z*sin(θ)  (2)

where Xh and Yh are Earth's magnetic vector projections to thehorizontal plane. Once Xh and Yh are known, it is possible to calculatean azimuth angle as:

azimuth=arcTan(Yh/Xh)  (3)

To facilitate the use of the accelerometer sensor as a tilt sensor, aknown low-pass filter may be applied.

In use, upon pressing the “start” button on the probe handle, theprocessing means 7 is supplied with all angle readings and calculatescurrent azimuth angle to set this azimuth angle as a azimuth referenceangle equaling to zero. At the same time, an orientation closeness ofazimuth angle discontinuity to this azimuth reference angle iscalculated. In case this closeness exceeds a predetermined threshold,axes X and Y are mutually changed in equations (1), (2) to move away theazimuth angle discontinuity from a probe operation range. All azimuthangles thereafter and during prostate examination procedure arecalculated relative to that azimuth reference angle so that the user mayobserve in real time all probe orientation angles: azimuth, elevation,and rotation.

FIG. 5 represents a schematic diagram of an electronic unit 6 of thedevice in accordance with the present invention. A plurality of pressuresensors 31 forming the head pressure sensor array 1, and a plurality ofpressure sensors 32 forming the shaft pressure sensor array 3 are shownon the diagram. A pressure sensing circuit inside the electronic unit 6comprises an analog switching unit 45, amplifier 46, converter and/orintegrator 49, designed to amplify and convert respective electricalsignals generated by each pressure sensor for detecting a pressureimposed on each sensor during prostate examination. Analog-to-digitalconverter 48 transforms analog input signal into a digital signal andsends it to a processor 52. A plurality of amplifiers 43 amplify signalsgenerated by accelerometer sensor 25 and magnetic sensor 26 describedabove for detecting the probe orientation during pressing against theprostate and movement of the probe from one pressing site to another.The amplified signals from amplifiers 43 are sent to multiplexer 47.Multiplexed signals are converted to digital signals byanalog-to-digital converter 51 and sent to processor 52. A set/resetcircuit 44 controlled by the processor 52 generates set/reset pulsessupplied to magnetic sensor 26 to optimize the magnetic domains for mostsensitive performance. Structure and functional characteristics ofset/reset circuit 44 are determined by the type of magnetic sensor usedfor the design of the probe and by recommendations of specific magneticsensor manufacturer. A control button 23 mounted on the transrectalprobe handle is connected to the processor 52 through a driver 50 forcontrolling the prostate examination process and providing at least astop/start function. Processor 52 communicates with analog-to-digitalconverters 48 and 51, multiplexers 45 and 47, and a communication port54 to support data exchange with external processing and displayingmeans 55. Preferably, the external processing and displaying means 55 isa compact laptop computer. Data storage unit 53 may be used inelectronic unit 6 for storing prostate examination data and intermediateinformation needed for proper functioning thereof, for exampleorientation sensor calibration data, pressure sensor calibration andtuning data, etc. The processing means is designed to automaticallydetect pressure sensors malfunction such as for example excessive noiseand impaired sensitivity and excludes any defect sensor data fromacquired pressure data frames.

The external processing and displaying means 55 is intended to serve forexamination data processing. It is adapted to perform the followingfunctions:

-   -   calculate the position of each pressure sensor during prostate        examination,    -   approximate and correct mechanical images of the prostate and        surrounding tissues,    -   separate and analyze the prostate mechanical images,    -   determine the prostate geometrical features and mechanical        features of prostate inner structures such as lesions, nodules,        stiffer tissue and the like, and    -   prepare the prostate images for visualization, as described        below.

The displaying means 55 preferably has a touch screen functions tocommunicate with the device during prostate examination.

FIG. 6 is a flow chart describing steps for obtaining diagnosticinformation in accordance with the present invention. Head pressuresignal is first acquired from the probe head pressure sensor array andthen transformed into head pressure response data 61 expressed forexample in kPa according with the sensor calibration characteristics.After temporal and two-dimensional spatial filtering in block 62, thedata is displayed for the user (in block 63) in real time duringprostate examination. It allows the user to guide the probe helping indetection of any abnormal or suspicious sites in the examined prostate.Shaft pressure signal is acquired from the probe shaft pressure sensorarray and transformed into a shaft pressure response data 65 expressedfor example in kPa according to the sensor calibration characteristics.After a temporal and two-dimensional spatial filtering in block 66, itis also displayed (block 67) in real time during prostate examination.This allows visualizing a part of sphincter area to guide the user infinding prostate and assisting in the probe navigation. Orientation data70 is acquired from the probe orientation sensors. Further, aftercalculation of azimuth, elevation and rotation angles in block 71, theseangles are displayed (block 72) in real time during the prostateexamination to guide the user in probe navigation.

After locating the prostate under the probe head pressure sensor array,the user presses the examination start/stop button on the probe handleto start a real time prostate mechanical image composition algorithm(block 68). Description of this algorithm is given below in explanationsof FIG. 9. The two-dimensional prostate mechanical image is composed anddisplayed in block 73. Simultaneously, the prostate examination dataincluding that pressure response and probe orientation data areaccumulated in block 64. All operations in block 60 take place in realtime during prostate examination.

After completing the prostate examination, the user presses again theexamination start/stop button on the probe handle to stop the real timeprostate mechanical image composition algorithm, and to go toexamination data saving procedure in block 74. A three-dimensionalprostate mechanical image composition algorithm in block 75 is runningautomatically as described in detail below. The composedthree-dimensional mechanical prostate image may be visualized in block77. Prostate geometrical features and mechanical features are calculatedin blocks 76 and 78 respectively. Printout of the prostate examinationresults (block 79) includes a series of prostate mechanical imagesrepresenting the most distinctive prostate findings and quantitativeprostate data such as a size, symmetry, medium groove, lesion detectionclassifier outputs and alike.

FIG. 7 is a perspective view of a probe relative to an examined prostateillustrating a reference coordinate system having three orthogonal axesand probe orientation angles. A processing means defines the referencecoordinate system X, Y, Z at the moment of first capturing a prostatemechanical image when a total pressure prostate signal exceeds apredetermined threshold after pressing the start examination button onthe probe handle. The following instant orientation angles are definedas reference angles for the reference coordinate system X, Y, Z:elevation (80), azimuth (81), and rotation (82). All subsequent probeorientation angles relative to the reference system X, Y, Z arecalculated relative to these reference angles. The probe head 21 ispressed against the prostate 4, when the first capturing a prostatemechanical image occurs. In a preferred method of the invention, a proberotation angle should be maintained close to zero. Despite of thepresence of the probe head pressure sensing surface curvature, themechanical image projection along X-coordinate on X, Y-plane is donewithout taking into account that curvature. The probe head mechanicalimage is acquired as a 2D image and used for prostate imagereconstruction inside a defined three-dimensional prostate volume. Forthe simplicity of real time calculations, the two axes X and Y of thereference coordinate system X,Y,Z are positioned in the mechanical imageplane of the probe head pressure sensor array, while the third referenceor Z-coordinate is perpendicular to the mechanical image plane.

FIG. 8 is a flow chart describing the steps necessary for composition ofa two-dimensional and a three-dimensional prostate mechanical image andcalculating prostate features. These algorithms can be activated in realtime during prostate examination as marked by dashed line 83 or afterthe examination is complete when all examination records are available(block 64). The first step is includes extraction of continuous pressuredata sequence from the head pressure sensor array by means forcalculating an individual two-dimensional pressure data frame when theprostate is located under the probe head, so that this data will only beused in prostate image composition. The extraction may be doneautomatically or manually by looking at examination process dynamics.Another purpose of this extraction is to exclude sphincter signals fromthe head pressure data during the probe insertion into the rectum.

The next step is done by the means for calculating of individualpressure imprints of the prostate on the transrectal probe of theinvention. Such means initiate detection of prostate pressure imprint ineach analyzed pressure data frame recorded from the head pressure sensorarray (block 84). These means include an algorithm, which estimates theprobability that mechanical image has a pressure signal increase in itscentral part. The possibility that some sensors could produce anerroneous signal, as well as that some rows and column in the sensorarray could have incorrect tuning or calibrating are taken into account.Such column and row errors may cause false pressure jumps or gaps in thepressure data. For each interior row or column of the sensor array, thedetection algorithm calculates a pressure signal value relative to thelinear interpolation based on the boundary pressure. A predeterminednumber of points with highest and lowest pressure values are discarded.The positive or negative sign of the sum of remaining values defines thesign of the entire line. Each line (row or column) is assigned a certainweight, the highest for the central lines, and the lowest for boundarylines. If the sum of the weights for all lines with corresponding signsis greater than a predefined value, it is considered that the mechanicalimage contains the prostate imprint. The sum is then normalized to apredetermined range, using two scale parameters, which gives aquantitative estimation of the presence of a prostate imprint in themechanical image. If no prostate pressure signal was detected inside theanalyzed pressure data frame, this data frame is discarded. On theopposite, if the prostate pressure signal was detected, the nextprocedure in block 85 activates extraction of only the prostate pressureresponse data (pixels) inside analyzed pressure response data frame.

The procedure for isolation of a prostate image consists of separationof one or several relatively big coherent zones containing a relativelyhigh pressure signal. Another purpose of this procedure is to reduce theinfluence of boundary effects and suppression of pressure peaks in thetop and bottom parts of the sensor array corresponding to the sphincterand bladder pressure signals. This procedure starts with quadrupling thenumber of pixels in the image using two by two interpolations betweenneighboring sensors. The binary image of the pressure pattern is createdby setting all pixels for which the pressure is higher than average toblack. At the same time, the pixels for which the pressure is lower thanaverage are set to white. Two types of filtering are applied thereafterto the binary image. The expanding filtering calculates the number ofblack pixels adjacent to each white point. If the number is higher thanthe predetermined value, it turns the white point into a black point inorder to enlarge the black regions and cover small white holes. Thesqueezing filtering is applied next to achieve the same but oppositeeffect for black points. It calculates the number of white pixelsadjacent to each black point. If that number is higher than thepredetermined value, it turns it to the white point in order to squeezeblack zones and smooth their edges. A sequence of expanding andsqueezing removes or significantly reduces small boundary defects,eliminates the inner white holes, combines and rounds large insidezones. The resulting black zone is mapped back to the pressure sensorarray, and only the pressure sensors, which belong to the black zone,are allowed to participate in the next phase of prostate image analysis.

Important advantage of the present invention is its ability to use theprostate itself as a reference object. After determination of prostateimprints earlier in the sequence, this is accomplished in the next fewsteps by the means for constructing of the composite prostate image.Specifically, in the procedure 86 the first n− frames of pressureresponse data are captured to construct a first pass two-dimensionalmechanical prostate structure. This capture is occurring when the totalpressure prostate signal exceeds a predetermined threshold. Afteraveraging, the captured first pass prostate structure is transferredinto a two-dimensional composite prostate image 91. After that, eachsubsequent pressure response data frame carrying the prostate pressureresponse data is analyzed in blocks 90 and 94 for placing new pressureresponse information into the two-dimensional composite prostate image.Block 90 runs a matching algorithm trying to find best fit of a currentprostate pressure response image inside the two-dimensional compositeprostate image. Preferably, the best fit is calculated by maximizing afunctional F

$\begin{matrix}{{{F\left( {n,m} \right)} = {{\sum\limits_{i,{j = 0}}^{{i = k},{j = l}}{S_{i,j}*P_{{n + i},{m + j}}\mspace{14mu} {for}\mspace{14mu} n}} \Subset \left( {{{- k}/4},{{+ k}/4}} \right)}},\mspace{14mu} {m \Subset \left( {{{- l}/4},{{+ l}/4}} \right)}} & (4)\end{matrix}$

where k and l are quantities of horizontal and vertical pixels insidethe pressure frame with the current prostate mechanical image, n and mare maximum possible image shift in pixels relative to a previous fittedmechanical image, S_(i,j) is current pressure response signal of i,jpixels, and is a pressure signal of n+i,m+j pixel inside thetwo-dimensional composite prostate image.

After the best fit is found, each pixel of a current mechanical prostateimage is placed into the two-dimensional composite prostate image with apredetermined weighted factor if its current value exceeds respectivepixel value inside the two-dimensional composite prostate image (block94). Preferably, all calculations in blocks 86, 90, 91, and 94 areimplemented with normalized pixels, so that each pixel value of theprostate mechanical image is divided by a modified average of analyzedpressure data frame calculated inside block 87. The modified average Sis calculated according to equation (5) after removing a predeterminedquantity (b) of pressure pixels S^(max) having maximum values.

$\begin{matrix}{\overset{\leftharpoonup}{S} = {\left( {{\sum\limits_{i,{j = 0}}^{{i = k},{j = l}}S_{i,j}} - {\sum\limits_{q = 0}^{q = b}S_{q}^{\max}}} \right)/\left( {{k*l} - b} \right)}} & (5)\end{matrix}$

where k and l are quantities of horizontal and vertical pixels insidethe pressure response frame with the analyzed prostate mechanical image,S_(i,j) is an instant pressure signal of i,j pixels.

Azimuth, elevation, and rotation angles calculated for the instantpressure response data frame in block 93, and evaluated Y-coordinatefrom shaft pressure data in block 89 are used in finding a frame localreference position inside the two-dimensional mechanical image space tostart matching algorithm in the accordance with equation (4).Simultaneously, a procedure 95 of removing image distortion andprocedure 96 of correction of the two-dimensional mechanical image 91are run during prostate examination. The procedure 95 smoothes anydistortions above a predetermined threshold in the calculated atwo-dimensional gradient field inside the image 91. Procedure 96corrects a prostate form if prostate form distortion exceeds the boundsof an acceptable prostate form variety.

Each pressure data frame carrying a prostate image is included into athree-dimensional mechanical prostate image 92 in accordance withpositioning in X,Y-plane as calculated in block 90 and Z-coordinate,which is considered proportional to the calculated in block 87 modifiedaverage for current frame 87. More detailed description of thethree-dimensional image composition algorithm of this block is givenbelow in the description for FIG. 10.

After prostate examination is complete, a procedure 97 of a finalsmoothing and three-dimensional interpolation is applied to currentimage 92. The final two-dimensional and three-dimensional mechanicalprostate images are then prepared in block 98 representing a pluralityof contour, slices, iso-surfaces and alike for a better visualperception. Such prostate features as prostate size (small/medium/large)102, medium groove (absent/present) 103, prostate shape(symmetrical/asymmetrical) 104 are calculated directly from the finalprostate image by testing these value to a predetermined acceptancecriteria.

A nodule classifier includes three nodule detectors. First of them,shown in block 99, analyzes a signal distribution for prostate pressuredata to detect specific features typical for a positive nodule presence.Second nodule detector, shown in block 100, applies a series ofpredetermined convolution filters to each two-dimensional prostatemechanical image to detect a nodule from a variety of possible noduleforms. Preferably, a form of a convolution filter corresponds to what isbeing looked for in a nodule form. A third nodule detector, shown inblock 101, applied a series of three-dimensional convolution filters tothe final three-dimensional prostate image in block 98. Presence ofspecific three-dimensional objects inside a filtered prostate imagesignals a possible nodule presence and its location.

FIG. 9 is an illustration of a sample real time two-dimensional prostateand sphincter area mechanical image with a relative probe positioning toguide the user during prostate examination. Multiple pressings of probehead 21 against the prostate 4 allow the head pressure sensor array toobtain pressure response data for the prostate. This pressure responsedata is then transformed into a composite two-dimensional mechanicalprostate image 109 as described in FIG. 8 (block 91). At the same time,the shaft pressure sensor array provides supplemental mechanical datafor the sphincter area, which is visualized in the same image frame 106as a two-dimensional sphincter mechanical image 110. Using procedures inblocks 89, 90, and 93 described in FIG. 8, current coordinates 107, 108of a probe head center 111 in the reference coordinate system X, Y, Z,as well as probe azimuth angle 113, and distance 112 between a sphinctercenter and the probe center 111 are then calculated. Combinedvisualization of the prostate image 109, the sphincter image 110 and theprobe head position facilitates the prostate probe navigation andprovides efficient feedback to the user.

Since orientation tracking system of the present invention provides onlyorientation angles including azimuth angle 113, it is important to usethe shaft pressure sensor array to detect the position of the sphinctercenter and use it as a reference point to calculate the movements of theprobe head. Initial position of the probe is assigned the azimuth anglevalue of zero as corresponding to the first pressing of the probe headagainst the prostate. Knowing the distance between the sphincter centeras detected by the shaft sensor array and the current azimuth angle 113,the new coordinate of the probe head can be calculated from thatdistance by multiplying it by sinus of the azimuth angle value.

FIG. 10 is an illustration of a three-dimensional prostate mechanicalimage composition in accordance with the method of the presentinvention. The three-dimensional prostate mechanical image 114 (see alsothe description of block 92 in FIG. 8 above), includes a plurality oftwo-dimensional mechanical prostate images 115, 117, 120 placed insideplanes 116, 118, 119 accordingly. During prostate scanning by multiplepressings of probe head 21 against the prostate 4, the head pressuresensor array provides pressure response data for the prostate. Each newpressure response data frame is transformed into a two-dimensionalmechanical prostate image in the accordance with procedure 85 and X,Y-frame coordinates for example 107, 108 as calculated by procedure 90and Z-coordinate as calculated by procedure 87 from FIG. 8. Each pixelof this pressure response data frame is then placed inside atwo-dimensional mechanical prostate image for example 117 with apredetermined weighted factor if its current pixel value exceeds athreshold value inside the two-dimensional prostate image 117.Preferably, two different three-dimensional mechanical prostate imagesare constructed: one image includes only normalized pressure responsepixels (each pixel value of the prostate mechanical image is divided bya modified average of analyzed pressure response data frame), whileanother image includes only absolute pressure response pixels.

The presence of the shaft sensor array can also be used for teachingpurposes using either patient models or practicing live prostateevaluations. Low contact forces between the probe and the tissues aboutthe patient's rectum is the goal of such training in order to minimizepatient's discomfort. Shaft pressure sensor array may be successfullyused to measure the level of various forces implied by the probe on thesphincter and other tissues and organs (with the exception of theprostate itself). These forces can be displayed in real time for theuser so that adjustments to the position of the probe can be made tominimize such forces during the examination.

Although the invention herein has been described with respect toparticular embodiments, it is understood that these embodiments aremerely illustrative of the principles and applications of the presentinvention. It is therefore to be understood that numerous modificationsmay be made to the illustrative embodiments and that other arrangementsmay be devised without departing from the spirit and scope of thepresent invention as defined by the appended claims.

1. A transrectal probe for mechanical imaging of a prostate comprising:a probe head sized to fit inside a rectum and equipped with a headpressure sensor array, said probe head having a distal end and aproximal end, said probe head defining a longitudinal probe head axis,and a probe shaft defining a longitudinal probe shaft axis, said probeshaft having an S-shaped distal end attached to said proximal end of theprobe head, said S-shaped distal end defining a linear offset betweensaid longitudinal probe head axis and said longitudinal probe shaftaxis, whereby said S-shaped distal end of said probe shaft configured tominimize disturbance of surrounding tissues and organs when saidprostate is compressed by said probe head during examination procedure.2. The transrectal probe as in claim 1, wherein said probe headincluding a straight segment containing said head pressure sensor array,said straight segment being about 25 mm (1 inch) to about 50 mm (2inches) long.
 3. The transrectal prove as in claim 1, wherein saidlinear offset ranging between about 4 mm ( 5/32 of an inch) and 15 mm (19/32 of an inch).
 4. The transrectal probe as in claim 3, wherein saidlinear offset is about 10 mm (⅜ of an inch).
 5. The transrectal probe asin claim 1, wherein said S-shaped distal end of the probe shaft shapedto define an angular offset between said longitudinal probe head axisand said longitudinal probe shaft axis.
 6. The transrectal probe as inclaim 5, wherein said angular offset ranging between about 4 degrees and12 degrees.
 7. The transrectal probe as in claim 1, wherein said probeshaft further including a shaft pressure sensor array, said headpressure array spaced away from said shaft pressure sensor array byabout 40 mm (1 9/16 inches) to 80 mm (3⅛ inches) as measured between thecenters of the respective pressure sensor arrays.
 8. A dual-arraytransrectal probe for mechanical imaging of a prostate, said probecomprising: a probe head sized to fit inside a rectum and equipped witha two-dimensional head pressure sensor array, and a probe shaft attachedto said probe head, said probe shaft including a shaft pressure sensorarray.
 9. The dual-array transrectal probe as in claim 8, wherein saidshaft pressure sensor array comprising at least one linear pressuresensor array.
 10. The dual-array transrectal probe as in claim 9,wherein said shaft pressure sensor array comprising at least two linearpressure sensor arrays.
 11. The dual-array transrectal probe as in claim10, wherein said shaft pressure array comprising three linear pressuresensor arrays.
 12. The dual-array transrectal probe as in claim 11,wherein said three linear pressure sensor arrays are parallel to eachother and to said probe shaft and spaced equally about the peripherythereof.
 13. The dual-array transrectal probe as in claim 8, whereinsaid shaft pressure sensor array is a two-dimensional pressure sensorarray.
 14. A dual-array transrectal probe system for mechanical imagingof a prostate comprising: a probe head sized to fit inside a rectum andequipped with a two-dimensional head pressure sensor array adapted toobtain a head pressure response data when said probe head is pressedagainst said prostate, a probe shaft attached to said probe head to forma transrectal probe, said probe shaft including a shaft pressure sensorarray adapted to obtain a shaft pressure response data, an electronicunit connected to said transrectal probe and adapted to receiving saidhead and shaft pressure response data, and a processing and displaymeans connected to said electronic unit, said processing and displaymeans further including a means for generating a mechanical image ofsaid prostate from at least said head pressure response data, a meansfor calculating the position of a sphincter from said shaft pressureresponse data, and a means for simultaneous displaying in real time ofsaid mechanical image of the prostate and said position of the sphincterspaced apart from said prostate during the examination thereof.
 15. Thesystem as in claim 14, wherein said probe head further includingorientation tracking means adapted to provide positional and angulardata of the location of said probe head.
 16. The system as in claim 15,wherein said means for generating said mechanical image of said prostatefurther including means for tracking the position and direction ofmovement of said probe head from said orientation tracking means incombination with said shaft pressure response data.
 17. The system as inclaim 14, wherein said means for locating the position of said sphincterincluding means for generating at least a two-dimensional mechanicalimage of said sphincter.
 18. The system as in claim 14 further equippedwith an alarm means indicating excessive compression force, said alarmmeans triggered when said shaft pressure response data exceeds apredetermined level of sphincter pressure force.